This PDF file contains the front matter associated with SPIE Proceedings Volume 9140, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

We present our results on optical absorption enhancement in crystalline silicon (c-Si) absorber structured with transversely quasicrystalline lattice geometry for thin-film photovoltaics. c-Si nanoarchitectures are prepared on the nanoimprinted ten-fold symmetry quasicrystalline textured substrate. The structural features of the fabricated Si nanostructures are analyzed to confirm the defining characteristics of the quasicrystalline texturing of the absorber film. We present the optical absorption plots for a spectrum of incident light for varying angle of light incidence in these fabricated higher symmetry crystalline Si architectures. Neither any back reflector nor antireflection coating is considered in the present study, where use of such layers could further improve the light absorption. The realized quasicrystalline textured silicon nanoarchitectures with higher rotational symmetry lattice geometry are observed to improve the isotropic and broad band absorption properties of the thin film c-Si absorber and envisaged to have efficiency enhanced thin film photovoltaics effective in terms of cost and performance.

A new generation of polycrystalline silicon thin film solar cells is currently being developed in laboratories, employing a combination of novel laser or electron beam based liquid phase crystallization (LPC) techniques and single side contacting systems. The lateral grain size of these polycrystalline cells is in the millimeter range at an absorber thickness of up to 10 μm. In this contribution we present a comparative simulation study of several 1D, 2D and 3D nano-optical designs for the substrate / illumination side interface to the several micrometer thick back contacted LPC silicon absorber material. The compared geometries comprise multilayer coatings, gratings with step and continuous profiles as well as combinations thereof. Using the transfer matrix method and a finite element method implementation to rigorously solve Maxwell’s equations, we discuss anti-reflection and scattering properties of the different front interface designs in view of the angular distribution of incident light.

We report on the power conversion efficiency (PCE) enhancement for organic solar cells (OSCs) based on several approaches. A standard cell composed of an indium tin oxide (ITO) anode, P3HT/ PCBM active layer, PEDOT:PSS hole transport layer and an aluminum cathode is used as a reference. We investigate the effects of the following three modifications. We first incorporate CdSe quantum dots (QDs) in the photo-optically active P3HT/PCBM blend in order to enhance the optical absorption. In opposite to other studies, QDs are not used here to replace the donor material (PCBM), and we always measured an enhanced PCE compared to the standard cell with a QDs:P3HTPCBM volume ratio up to 1:5. As a second modification, NaYF₄:Yb,Er up conversion (UC) microcrystals are incorporated into a TiO_2-x sol-gel to form an additional layer used to convert IR photons to blue and green photons. Again, OSCs with UC layer showed an improved PCE compared to the reference cell. The PCE enhancement is both attributed to the IR light absorption and to a better electron transport between the active layer and the cathode due to the electron transport layer capabilities of TiO_2-x. Finally, MoO₃ layer is used to replace the PEDOT:PSS layer as hole transport layer (HTL). This layer is deposed either by thermal evaporation or by spin coating from a sol-gel solution. We found evaporation better in terms of thickness control and reproducibility. It has been demonstrated that the PEDOT:PSS HTL can be replaced by MoO₃, and the thickness of this MoO₃ layer strongly affects the PCE of the cell. The maximum PCE was obtained with a thickness of 40nm, and again is better that the reference cell.

The key issue for enhancing the efficiency of semiconductor photovoltaic material devices is to reduce point defects recombination phenomena and to extend the absorption wavelength range. By inserting InAs Quantum Dots in a host GaAs semiconductor structure, new energy levels can be generated resulting in wavelength absorption enhancement. Thus, the main objective of this work was to design a material based on GaAs host semiconductor with extended absorption wavelength in the infrared region. We extend our previous characterisation of GaAs/InAs material systems by studying variable temperature photocurrent spectroscopy from 300K down to 50K in order to study the effect of different inter-dot doping profiles on cell efficiency.

The possibility to increase the efficiency of solar cells by a restriction of the maximal angle of emission has been proposed for several times. Typically, this is achieved by applying a directionally selective filter on top of the solar cell. This filter leads to a reflection of emitted light under certain angles back into the cell, where it then can be reabsorbed. A system where the emission process itself is inhibited for certain angles (photonic solar cell) is in principle a better system, because then optical losses in the system can be suppressed as the emission in fact does not take place. In this contribution, we focus on a photonic solar cell, where the cell and the filter are combined in one single optoelectronic device. This means that the solar cell itself has a photonic structure or is implemented into a photonic crystal. The interesting question is how such a device could look like and how it performs. Here, design concepts for photonic solar cells are shown and simulated optically. An interesting system could be an integration of a solar cell as defect layer into a thin film stack. To get an idea of the potential of such systems, the emission out of a photonic solar cell has to be compared to the emission out of a standard solar cell. To this end, a scattering-matrix-formalism is used. First estimations of the possible system efficiencies are given as indication of the system quality.

Crystalline silicon solar cells absorb light in the near infrared only weakly. To utilize also the infrared light of the solar spectrum with energies still greater than the band gap of silicon, the effective path of the light inside the solar cell has to be enhanced. Light paths can be manipulated at the front side as well as at the rear side of a solar cell. For the front side, pyramidal textures that also show anti-reflection properties are widely used. These anti-reflection properties, however, can also be achieved with planar dielectric coatings or nanostructured surfaces. In this case, the path length enhancement can be achieved with rear side structures that are especially optimized for this purpose, thus de-coupling anti-reflection and path-length enhancement functionalities. This de-coupling creates leeway to optimize not only the optical properties but also the electrical properties of the optically active structures, and to realize structures that are compatible with very thin silicon wafers. To this end, this paper investigates two kinds of diffractive rear side structures, both, theoretically and experimentally. First, hexagonal sphere gratings that are produced by a self-organized growth process using spin coating, and second, binary gratings produced via nano-imprint lithography. Both process chains are potentially scalable to large areas. In optical measurements we determined potential photocurrent density gains of over 1 mA/cm² for 250 μm thick wafers for both structures. Furthermore, we developed a process for contact formation as one key step to fully processed solar cells with diffractive rear side structures.

In this study, we experimentally investigate the light-trapping effect of plasmonic reflection grating back contacts in prototype hydrogenated amorphous silicon thin-film solar cells in substrate configuration. The plasmonic reflection grating back contacts consist of periodically arranged Ag nanostructures on flat Ag reflectors. By varying the geometrical parameters of these back contacts, design strategies for optimized light trapping are identified. First, a general correlation between a reduction of the period of the plasmonic reflection grating back contact and an increase of the absorptance as well as external quantum efficiency is found for various unit cells of the nanostructures i.e. square unit cell, hexagonal unit cell and face-centered unit cell. Second, the width of the nanostructures is varied. With increasing width, an enhanced light-trapping effect of the thin-film solar cells is found independent of the period. As a result, an optimized design for improved light trapping in the studied thin-film solar cells is a combination of a period of 600 nm and a structure width of 350 nm. Solar cells fabricated on plasmonic reflection grating back contacts with this optimized configuration yield enhanced power conversion efficiencies as compared to reference solar cells processed on state-ofthe- art randomly textured substrates. In detail, the power conversion efficiency is enhanced by around 0.2 % from 9.1 % to 9.3 %. This increase is largely due to the enhancement of the short-circuit current density of around 7 % from 14.7 mA/cm² to 15.6 mA/cm².

Upconversion of sub-band-gap photons is a promising approach to increase the efficiency of solar cells. In this paper, we review the recent progress in upconverter material development and realization of efficient upconverter silicon solar cell devices. Current published record values for the increase in the short-circuit current density due to upconversion are 13.1 mA/cm² at a solar concentration of 210 suns determined in a sun simulator measurement. This increase is equivalent to a relative efficiency enhancement of 0.19% for the silicon solar cell. Although this is a considerable enhancement by more than one order of magnitude from values published only a few years ago, further enhancement of the upconversion performance is necessary. To this end, we investigate theoretically the application of resonant cavity and grating photonic structures. Our simulation based analysis considers irradiance enhancement and modified density of photon states due to the photonic structures and their impact on the upconversion dynamics in β-NaYF₄: 20%Er³⁺. It shows that an optimized grating can increase upconversion luminescence by a factor of 3 averaged over the whole structure in comparison to an unstructured reference with the same amount of upconverter material.

For high band gap solar cells, organic molecule based upconverter materials are promising to reduce transmission losses of photons with energies below the absorption threshold. We investigate the approach of embedding the organic upconverter DPA:PtOEP directly into each second layer of a Bragg stack to achieve an enhancement of upconversion performance. The two major effects that influence the upconversion process within the Bragg stack are simulated based on experimentally determined input parameters. The locally increased irradiance is simulated using the scattering matrix method. The variation of the density of photon states is obtained from calculations of the eigenmodes of the photonic crystal using the plane wave expansion method. A relative irradiance enhancement of 3.23 has been found for a Bragg stack of 31 layers including λ/8-layers on both sides. For suppressing the loss mechanism of direct sensitizer triplet decay via variations of the density of photon states, a different design of the Bragg stack is necessary than for maximum irradiance enhancement. In order to find the optimum design to increase upconversion quantum yield, both simulation results need to be coupled in a rate-equation model. The irradiance enhancement found in our simulation is significantly higher than the one found in the simulation of a grating-waveguide structure, which achieved an increase of upconversion quantum yield by a factor of 1.8. Thus, the Bragg structure is very promising for upconversion quantum yield enhancement.

Rare-earth doped borate glasses are investigated for their potential as photon down-shifting cover glass for CdTe solar cells. Note, that CdTe solar cells have a poor response in the ultraviolet and blue spectral range due to absorption in the CdS buffer layer having a band gap of 2.4 eV. The following trivalent rare-earth ions are analyzed in detail: Sm³⁺, Eu³⁺, and Tb³⁺. These ions provide strong absorption bands in the ultraviolet / blue spectral range and an intense emission in the red (Sm³⁺ and Eu³⁺) or green (Tb³⁺) spectral range. The gain in short-circuit current density of a CdTe solar cell is calculated for different rare-earth ion concentrations. The calculations are based on the rare-earth’s absorption coefficients as well as their photoluminescence (PL) quantum efficiency. For Sm³⁺, the PL quantum efficiency depends significantly on the doping concentration. Finally, the potential of double-doped borate glasses, i.e. glasses doped with two different rare-earth ions, is investigated.

Rare-earth ions embedded in glassy matrices are promising materials for photon upconversion processes, e.g. to convert near infrared light to frequencies above the band gap of a solar cell to make it available for electrical power generation. One strategy to optimize the efficiency of such upconversion processes is to embed the active ions in a host matrix with minimal losses to non-radiative relaxation. For the model system of trivalent neodymium in fluorochlorozirconate (FCZ) glass it has been shown recently that a uniform growth of BaCl₂ nanocrystals inside such glasses can decrease the probability of multi-phonon relaxation (MPR) drastically, leading to a huge increase in upconversion intensity for monochromatic illumination. To identify the key processes which may enhance or diminish the total upconversion efficiency, a comprehensive description for the optical dynamics of neodymium in FCZ glass ceramics has been developed on the basis of a rate equation system, including ion-photon, ion-phonon, and ion-ion interactions. An effective medium approach is utilized to account for the neodymium located in BaCl₂ nanocrystals or the FCZ glass bulk, respectively. The numerous parameters required to enable for a reliable numerical simulation of the processes are obtained from theoretical approaches like Judd-Ofelt theory, as well as from experimental studies of luminescence decay after femtosecond excitation at various wavelengths and luminescence spectra under cw illumination at 800 nm wavelength. This rate equation model enables for a convenient, self-consistent description of all time-resolved and cw experiments on samples with different neodymium concentration. On this basis, the power dependence of upconversion spectra can be simulated in good agreement with the experimental result for 800 nm cw illumination. The model therefore forms an excellent tool for optimizing the upconversion efficiency of rare-earth doped luminescent material also under realistic (broadband illumination) conditions.

We investigate light-scattering textures for the application in thin-film solar cells which consist of a random texture, as commonly applied in thin-film solar cells, that are superimposed with a two-dimensional grating structure. Those textures are called photonic random texture. A scalar optical model is applied to describe the light-scattering properties of those textures. With this model, we calculate the angular resolved light scattering into silicon in transmission at the front contact and for reflection at the back contact of a microcrystalline silicon solar cell. A quantity to describe the lighttrapping efficiency is derived and verified by rigorous diffraction theory. We show that this quantity is well suitable to predict the short-circuit current density in the light-trapping regime, where the absorptance is low. By varying the period, height and shape of the unit cell, we optimize the grating structure with respect to the total generated current density. The maximal predicted improvement in the spectral range from 600-900 nm is found to be about 3 mA/cm² compared to the standard random texture and about 6 mA/cm² compared to a flat solar cell.

Thin-film solar cells contain nano-textured interfaces that scatter the incident light, leading to increased absorption and hence increased current densities in the solar cell. In this manuscript we systematically study optimized random nano-textured morphologies for three different cases: amorphous hydrogenated silicon solar cells (a-Si:H, bandgap 1.7 eV), nano-crystalline silicon solar cells (nc-Si:H, bandgap 1.1 eV) and tandem solar cells consisting of an a-Si:H and a nc-Si:H junction. For the optimization we use the Perlin texture algorithm, the scalar scattering theory, and a semi-coherent optical device simulator.

In this contribution, we use a rigorous electro-optical model to study randomly rough crystalline silicon solar cells with the absorber thickness ranging from 1 to 100 μm. We demonstrate a significant efficiency enhancement, particularly strong for thin cells. We estimate the “region of interest” for thin-film photovoltaics, namely the thickness range for which the energy conversion efficiency reaches maximum. This optimal thickness results from the opposite trends of current and voltage as a function of the absorber thickness. Finally, we focus on surface recombination. In our design, the cell efficiency is limited by recombination at the rear (silicon absorber/back reflector) interface, and therefore engineering the front surface to a large extent does not reduce the efficiency. The presented model of roughness adds a significant functionality to previous approaches, for it allows performing rigorous calculations at a much reduced computational cost.

In solar thermophotovoltaic (STPV) generation systems, the thermal radiation from emitters heated by the high temperature solar absorbers is converted into electricity at a photovoltaic (PV) cell. STPV systems have some advantages over PV generation systems. For instance, it is possible to control the thermal radiation spectrum of the emitter. Generally, the PV cell has an inherent sensitive region where an incident photon excites the electron. Enhancing the thermal radiation in this sensitive region of the PV cell, therefore, increases the generation efficiency. Theoretically, the efficiency of STPV systems can reach up to 85% when Carnot efficiency is considered and up to 45% when a monochromatic radiation releasing emitter is used. However, the experimental STPV system is less efficient than theoretical one as a consequence of the large amount of heat loss from the high-temperature absorber/emitter system. The purpose of this study is to achieve a high-efficiency STPV generation system using a monolithic planar spectrally selective absorber/emitter. The temperature superiority of the monolithic planar absorber/emitter is estimated by using spectral and thermal properties of STPV system components. Using the enitre configuration of the STPV system, a system efficiency of over 10% is estimated in this study.

A new light-trapping concept is presented, which joins broad bandwidth volume phase reflection holograms (VPRH) working together with three other optical components: specifically designed three-dimensional (3D) cavities, Total Internal Reflection (TIR) within an optical medium, and specular reflection by means of a highly reflective surface. This concept is applied to the design and development of both low concentration photovoltaic (LCPV) and solar thermal modules reaching a concentration factor of up to 3X. Higher concentrations are feasible for use in concentrated solar power (CSP) devices. The whole system is entirely made of polymeric materials (except for the solar cells or fluid carrying pipes), thus reducing cost by up to 40%. The module concentrates solar light onto solar cells – or fluid carrying pipes – with no need for active tracking of the sun, covering the whole seasonal and daily incident angle spectrum while it also minimizes optical losses. In this work we analyze the first experimentally measured optical characteristics and performance of VPRH in dichromated gelatin film (DCG) in our concept. The VPRH can reach high diffraction efficiencies (∼98%, ignoring Fresnel reflection losses). Thanks to specifically designed raw material, coating and developing process specifications, also very broad selective spectral (higher than 300 nm) and angular bandwidths (∼+20º) per grating are achieved. The VPRH was optimized to use silicon solar cells, but designs for other semiconductor devices or for fluid heating are feasible. The 3D shape, the hologram’s and reflective surface’s optical quality, the TIR effect and the correct coupling of all the components are key to high performance of the concentration solar module.

We present a new solar concentrator concept. This concept is based on spectral splitting. It implies reflective, refractive and diffractive elements that allow two spectrally differentiated beams to reach different and/or unmatched lattice solar cells. The aimed geometrical concentration factor is 5× and the theoretical optical efficiency of that concentrator concept reaches theoretically 82%. The following study will discuss the concept of such a solar concentrator. A practical application to dye sensitized solar cells is given. The manufacturing and design of the element is then exposed. Those elements have been tested in the laboratory. Good agreements with theoretical simulations are demonstrated.

This experimental study was carried out within the context of high concentration photovoltaics. The paper presents the results of an experimental investigation relating to the quantification of the impacts of the chromatic effect on the performance of a double junction GaInP/GaAs solar cell. Chromatic effects are the result of material dispersion caused by the refractive optics component. This study aims to evaluate the effect of the spectral modification of the incident beam on the whole solar concentrator system performance. Such considerations are fundamental in producing a highly accurate design, with which to achieve the best possible system performance. Efficiency is evaluated within the vicinity of the focus of a Fresnel lens designed for concentration. On the optical axis, rays with different wavelengths are not focalized at the same points. The spectral content of the beam depends, therefore, upon the position of the cell along the optical axis. It is assumed that spectral content modification may have an impact on cell performance and, as a consequence, on system efficiency as a whole. Efficiency of the optical Fresnel lens and of the cell were evaluated in relation to spectral content modification.

The design concepts of an ecofriendly water-repellent film using the sugar-related organic compounds with fluorinated alkyl group derived from biomass are demonstrated to avoid various kinds of nanoimprint material pattern peeling, defects, particles, and contaminants in ultraviolet curing nanoimprint lithography. Developed sugar-related organic compounds with three glucose derivatives with ultraviolet curable groups or fluorinated alkyl group derived from biomass produced high-quality imprint images of pillar patterns with a 230-300 nm diameter and height of 200-250 nm. The ecofriendly waterrepellent film as a functional biomass material was indicated to achieve the high water contact angle of 102°, low surface free energy of 22.1, suitable refractive index of 1.42-1.50, and high transparency at the wavelength of 350-700 nm.

Metallic nanostructures revealing plasmonic effects are a promising approach for improved photon management in thin solar cells. Irregular structures, as found in literature, suffer from parasitic absorption as a result of the varying dimensions of the particles. The parasitic absorption can be minimized by realising regularly ordered particles. Our fabrication process, suitable to meet these requirements, is based on interference lithography (IL), UV nanoimprint lithography (UV-NIL) and lift-off. As a process capable of large area structure origination, we use IL for the realization of master structures. Combining IL with NIL as a replication technique, the process chain is very versatile concerning nanoparticle shapes, sizes and arrangements. In the UV-NIL process, a flexible silicone stamp, which was replicated from the master structure, is pressed into a resist, which is cross-linked by UV light. A plasma etching step is applied to remove the residual resist layer. Afterwards, the substrate is coated with a thin metal layer and finally a lift-off is carried out. This results in metallic nanoparticles arranged in a regular pattern on the substrate. We show simulations and experimental results of round and elliptical disks and half spheres arranged in crossed and hexagonal gratings on glass and silicon. The elliptical particles show polarization dependent resonance effects. In a model assisted parameter study, we demonstrate the influence of various structure parameters on the absorption enhancement in silicon. Finally, optical measurements of ordered silver nanoparticles on the rear side of a silicon wafer are shown.

Following pioneering works, the 3D hybrid lead-halide perovskites CH₃NH₃PbX₃ (X=Cl, Br, I) have recently been shown to drastically improve the efficiency of Dye Sensitized Solar Cells (DSSC). It is predicted to open “a new era and a new avenue of research and development for low-cost solar cells … likely to push the absolute power conversion efficiency toward that of CIGS (20%) and then toward and beyond that of crystalline silicon (25%)” (Snaith, H. J. Phys Chem. Lett. 4, 3623-3630 (2013).). Here, we investigate theoretically the crystalline phases of one of the hybrids relevant for photovoltaic applications, namely CH₃NH₃PbCl₃. Critical electronic states and optical absorption are thoroughly investigated both in the low and high temperature phases. Our findings reveal the dramatic effect of spin orbit coupling on their multiple band gaps. Their physical properties are compared to those of conventional semiconductors, evidencing inversion of band edge states.

Crystallization of amorphous hydrogenated silicon thin films with femtosecond laser pulses is a currently developable technique for nanocrystalline silicon production for optoelectronics applications. The significant drawback of this technology is the hydrogen losses upon laser treatment of the film, while certain hydrogen concentration is essential to obtain high-quality material. Therefore we aimed to study the effect of post-hydrogenation of laser-modified amorphous silicon films on their hydrogen content and photoelectric properties. Using laser pulses of different fluence we obtained two-phase films with different crystalline volume fraction up to 60%. Post-hydrogenation procedure was found to partially compensate hydrogen out-diffusion and remarkably increase photoconductivity of highly crystallized films. At the same time the contribution of nanocrystalline phase to the total films' photoconductivity substantially increases. The results points out the effectiveness of applied hydrogenation procedure for a production of laser crystallized amorphous silicon films with suitable properties for optoelectronics.

We report on the fabrication and measurement of ultrathin a-Si solar cells with plasmonic back contacts composed of nanopattern dendritic/shrub-like Ag nanostructures that exhibit enhanced short circuit densities compared cells with flat back contacts. The morphology of the Ag nanostructure can be well controlled by the reaction time. When the proposed structure was used in the solar cell. The back-reflector of solar cell can be well designed by various Ag nanostructures and periods. A one-dimension shrub-like Ag nanostructure with spacing of 600 nm, exhibited a 14 % increase in short-circuit current density and a 20% increase in energy conversion efficiency are observed. This study indicates that the dendritic/shrub-like Ag nanostructure can be applied as a enhancing conversion configuration for ultrathin a-Si solar cells.

Here we report the synthesis and physical characterization of four substituted phenylenevinylene molecules, 1-4, which serve as short chain model oligomers of poly(1,4-phenylenevinylene). Quantum mechanical calculations on alkoxy substituted stilbene derivatives 1 and 2 reveal a direct correlation between the torsional angles and the substituent pattern. HOMO and LUMO energy levels were calculated for all four compounds and showed that the introduction of alkoxy substituents reduce the energy gaps between the ground and first excited singlet states of these molecules. In addition, absorption spectra, fluorescence life-times and quantum yield data of the four compounds are presented.

We present results on direct pulsed laser interference texturing for the fabrication of diffraction gratings in ZnO:Al layers. Micro gratings of 20 micron diameter with a groove period of 860 nm have been written using single pulses of a 355 nm picosecond laser using a home-built two-beam interference setup. The groove depth depends on the local laser intensity, and reaches up to 120 nm. At too high pulse energies, the grooves vanish due to surface melting of the ZnO. The fast scanning stage and the high repetition rate laser of a laser scribe system have been used to write grating textures of several cm² in ZnO:Al films with a surface coverage of about 80%. A typical laser written grating texture in a ZnO:Al film showed a haze value of about 9% at 700nm. The total transmission of the film was not lowered compared to the film before texturing, while the sheet resistance increased moderately by 15%. A-Si:H/μc-Si:H solar cells with laser textured ZnO:Al front contact layers so far reach an efficiency of 10% and current densities of 11.0 mA/cm², and 11.2 mA/cm² for top and bottom cell, respectively. This is an increase of 16% for the bottom cell current as compared to reference cells on planar ZnO:Al. The voltage of the laser textured cells is not reduced compared to the reference cell when slightly overlapping laser pulses of reduced pulse energy are applied. This method allows to write textures in ZnO:Al films that e.g. have been deposited with strongly varying deposition conditions, or cannot be texture etched in HCl. The method can be improved further by using 2D periodic patterns and optimizing the groove pitch, and may be applicable also to other solar cell technologies.

For an optimized light harvesting while using diverse periodic photonic light-trapping architectures in low cost thin film crystalline silicon (c-Si) solar cells, it is also of prime importance to tune the features of their lattice point basis structure. In view of this, tapered nanoholes would be of importance for envisaged better light in-coupling due to graded index effect and also from the point of fabrication feasibility. Using a 3D finite element method based computational simulator, we investigate the basis structural influence of triangular as well as honeycomb lattice-structured experimentally feasible tapered air nanoholes in ~400 nm thick c-Si absorber on a glass substrate. We present a detailed convergence analysis of volume absorption in Si absorber with cylindrical as well as tapered nanoholes. For a wavelength rage of 300 nm to 1100 nm, we present the computed results on light absorption of the engineered Si nanoholes for a lattice periodicity of 600nm. In particular, we study the influence of tapering angle of engineered nano air holes in Si thin film for the absorption enhancement in photonic triangular and honeycomb lattice structured tapered nanoholes. Further we make a comparative analysis of cylindrical and tapered nanoholes for a range of light incident angles from 0° to 60°. For the presented triangular as well as honeycomb lattice structured nanoholes, we observe that in comparison to the cylindrical nanoholes, the tapered nanoholes perform better in terms of light trapping for enhanced light absorption in textured Si thin films even when the effective volume fraction of Si is lower in the absorber layer with tapered nanoholes in comparison to that of cylindrical ones. From the maximum achievable short circuit current density estimation in the present study, the performance of c-Si absorbing layer engineered with triangular lattice structured tapered air holes harvests light efficiently owing to its higher lattice symmetry among periodic structures as well as graded index effect of the tapered nanoholes.